Glycol ethers are widely used as hydraulic fluids, especially as brake fluids. One disadvantage of glycol ethers in such systems is their relatively high viscosities at low temperatures (e.g., -40.degree. F.) which results in poor response of the system at low temperatures. Another disadvantage of glycol ethers is their tendency to absorb water. Water so absorbed tends to volatilize at high temperatures causing the hydraulic system to "vapor lock".
It has been proposed to employ various organosilicone materials as hydraulic fluids in lieu of glycol ethers. However, organosilicone materials have not proven particularly satisfactory as hydraulic fluids to date. By way of illustration, silicone oils [i.e., materials having the formula Me.sub.3 SiO(Me.sub.2 SiO).sub.x SiMe.sub.3 ] tend to shrink SBR rubber gaskets often present in hydraulic systems with resulting leakage of the silicone oil from the system. Moreover, silicone oils have relatively poor lubricity for the metals conventionally used in hydraulic systems and hence relatively high wear is encountered when silicone oils are employed in such systems. As a further illustration amino-organosilicones have been proposed as hydraulic fluids. However, such materials are relatively expensive and have relatively low wet boiling points which is indicative of a tendency of hydraulic systems containing such materials to vapor lock at high temperatures under humid conditions.